Research presented this week at a medical conference indicates that metal-on-metal hip replacement devices implanted in thousands of people are ticking time bombs. According to a report from USA Today, a growing number of studies indicate that the debilitating health problems associated with metal-on-metal hip implants could persist for years.

It is believed that metal-on-metal hip implants can shed dangerous amounts of cobalt and chromium through wear, leading to tissue damage, premature device failure, the need for revision surgery, and even long-term health problems, including heart and nervous system damage. Last May, the U.S. Food & Drug Administration (FDA) directed 21 makers of all-metal hip implants, including DePuy, to conduct post-market studies of their products to determine if they were shedding dangerous amounts of metallic debris in patients.

According to the American Society of Hip and Knee Surgeons, nearly 40,000 people in the U.S. received metal-on-metal hip implants in a single year, 2005 through 2006, accounting for 40% of all hip replacements during that time. It is now estimated that some 500,000 people have the devices.

“This is a serious problem in the USA,” Mathias Bostrom, an orthopedic surgeon at the Hospital for Special Surgery in New York City, told USA Today. “Some implants have a worse record than others, but almost all the metal-on-metal implants have issues.”

Bostrom was attending the American Academy of Orthopaedic Surgeons in San Francisco, where the issues surrounding metal-on-metal hip implants is a hot topic of discussion.

Another attendee, Joshua Jacobs, chairman of orthopedic surgery at Rush Medical College in Chicago, told USA Today that because of their issues, the use of metal-on-metal hips has decreased dramatically. He also cautioned that “It is important for anyone with a metal-on-metal implant to follow up with their orthopedic surgeon.”

Some of the research linking metal-on-metal hip implants reviewed at the conference included a study out of the Netherlands which found that 202 of 614 (32%) metal-hip implant recipients had suffered adverse reactions in soft tissue. An English study found that 24% of metal-on-metal hip implant patients who had revision surgery for a failed device had “worsening symptoms.” A third of those patients underwent a second revision surgery due to their issues, and disease progression “was confirmed in all cases of re-revision,” the authors wrote. Finally, an orthopedic surgeon from the Hospital for Special Surgery reported that a study he participated in found that 98% of the cups and 93% of the balls showed “moderate to severe scratching” in 46 retrieved metal-on-metal implants.

More bad news about metal-on-metal hips could be released in the near future. As we reported earlier this week, a study that may be presented next month at the British Hip Society meeting has purportedly found a possible link between cancer and all-metal hip implants. The study, conducted by researchers at the University of Bristol, involved 72 patients with the devices, and found that 17 had sustained genetic damage to the cells of the bladder, which could be a precursor to cancer. Three were found to have full-blown bladder cancer. That study has yet to be released, as an analysis of its findings is ongoing.